In forming a tire, there is used a mold which applies a pressure to the inside of a formed green tire and brings the outer surface of the green tire into pressure contact with the inner wall of the heated mold to vulcanize the green tire with heat and under pressure. On the internal surface side (on a tread side of the tire) of such a mold, a plurality of blades are provided for forming a tread pattern on the tire. The blades comprises circumferential groove forming blades (protruding streaks) for forming grooves being continuous in the circumferential direction of the tire, tread forming blades for forming tread grooves of predetermined shapes on the tread surface of the tire and sipe forming blades for forming sipes of a thin groove shape. Usually, a mold with a tread pattern formed thereon is divided into a plural number (for example, eight segments) in the circumferential direction.
Heretofore, electric discharge machines or the like have been used to form tread patterns by extra material cutoff machining. However, particularly, sipe forming blades for forming sipes take the form of a thin plate, and thus, difficulties arise in cutting them out. Thus, it has been conceived to form on a mold thin grooves for planting sipe forming blades and to secure the sipe forming blades to the mold after inserting the sipe forming blades into the thin grooves. As a mold of this kind, there has been known one which is described in, for example, Patent Document 1.
In the mold described in Patent Document 1, in order that the blades inserted into the thin grooves do not come off, each blade planting groove is formed at its bottom portion with a step portion having a greater thickness than the groove thickness of the groove, a U-shape notch is formed on each blade, and the portion surrounded by the notch is plastically deformed to form a bent portion, so that once the blade is inserted into the blade planting groove, the blade does not come off as a result of being engaged at the bent portion thereof with the step portion of the blade planting groove.